In general, a fastener is any device used to connect or join two or more components to create an assembly. In the field of manufacturing there are numerous assembly processes requiring individual components to be joined with fasteners to create an assembled product. Most of these processes, requiring fixations of one component in relation to another, are currently performed using threaded fasteners for connections. The most common threaded fasteners are referred to by many names, among them: bolts, screws, nuts, studs, lag screws, and set screws.
When a bolt is used to clamp two parts together, the force exerted between the parts is generally referred to as the clamping load. A clamping load is produced by exerting a rotational torque on a threaded fastener that is converted to linear travel via the helical threads. These forces keep the threads of the mating parts in intimate contact and decrease the probability of the fastener loosening in service. However, it is well known that threaded fasteners loosen over time when the part to which the fastener is affixed is subjected to shock or vibration. This is particularly true of threaded type fasteners used on devices with moving parts or in conjunction with motors or vehicles. To prevent this loosening, locking fasteners, lock washers, plastic inserts in the nut or bolt, adhesives, cotter pins, locking tabs, etc., are available to hold a threaded fastener in place until it is purposefully loosened. Most of these locking devices cooperate in one way or another with the head of the fastener.
However, in many fastening applications a typical bolt with a head cannot be used; for example, in situations where a head would limit the distance the bolt could be tightened into an aperture or where a protruding head on a moving or rotating part could damage equipment or personnel. In these situations, a set screw is typically used in place of a bolt. Devices such as lock washers cannot be used to hold headless fasteners in place and thus they are especially prone to loosening. A typical application for set screws is securing collars to shafts. In these applications, a set screw is tightened within a threaded aperture in a collar to apply pressure to the side of the shaft. Because the set screws are subjected to shock each time the shaft is started and vibration while the shaft is rotating, the set screws often loosen over time increasing the required machinery maintenance.
In the past, alternate methods for locking a set screw to a part, thereby preventing the screw from loosening have been employed. These methods include staking the set screw to the part, using plastic or elastomeric inserts to bind the threads, and the use of thread locking adhesives to adhere the threads of the set screw to the threads of the part. Each of these solutions has inherent problems associated therewith. Staking the set screw to the part requires prick punching the boundary between the set screw and the part. This method creates an unsightly surface on the part and, over multiple lockings, damages both the set screw and the part. Plastic inserts require additional and costly manufacturing processes and require the fastener to be replaced after one use. Using an adhesive substance with the set screw can destroy the set screw and clog threads in the part.
With reference to the field of orthopedic surgery there are various procedures which require insertion of an anchor, pin, peg, screw or cage into skeletal bone for the purpose of correcting anatomical defects. Related orthopedic procedures include reconstruction, such as the formation of artificial joints and teeth. All of these procedures, requiring fixations of an appliance in the bone, are currently performed using threaded connections between the components. For example, in many spinal corrections, pedicle screws are placed in the vertebrae to support cages or plates for fixing spatial orientation. The connection of the screws to the ancillary devices usually require concomitant application of torque to the vertebrae through the pedicle screw. Similarly, in placing artificial teeth on screw-like pegs inserted in the jaw bone, a particular degree of torque may be applied in the course of fitting of the teeth. Thereafter, attachment of auxiliary devices to the screw-like pegs, using fasteners that require torque, may be detrimental to the integrity of the pre-torqued screws securement within the bone.
Accordingly, what is lacking in the prior art is a cost effective internally disposed linear fastening system, particularly a locking set screw system capable of linear engagement. The set screw locking system should achieve objectives such as providing improved manufacturing and assembly efficiency, effective reliable performance, corrosion resistance, and torqueless locking assembly. The system should include packaging flexibility for installation on various products, including retrofitting existing product configurations with minimal modification of the original product.